Collision-Induced Broadband Optical Nonreciprocity

Open Access

Collision-Induced Broadband Optical Nonreciprocity

Chao Liang, Bei Liu, An-Ning Xu, Xin Wen, Cuicui Lu, Keyu Xia, Meng Khoon Tey, Yong-Chun Liu, and Li You

Phys. Rev. Lett. 125, 123901 – Published 14 September 2020

Abstract

Optical nonreciprocity is an essential property for a wide range of applications, such as building nonreciprocal optical devices that include isolators and circulators. The realization of optical nonreciprocity relies on breaking the symmetry associated with Lorentz reciprocity, which typically requires stringent conditions such as introducing a strong magnetic field or a high-finesse cavity with nonreciprocal coupling geometry. Here we discover that the collision effect of thermal atoms, which is undesirable for most studies, can induce broadband optical nonreciprocity. By exploiting the thermal atomic collision, we experimentally observe magnet-free and cavity-free optical nonreciprocity, which possesses a high isolation ratio, ultrabroad bandwidth, and low insertion loss simultaneously. The maximum isolation ratio is close to 40 dB, while the insertion loss is less than 1 dB. The bandwidth for an isolation ratio exceeding 20 dB is over 1.2 GHz, which is 2 orders of magnitude broader than typical resonance-enhanced optical isolators. Our work paves the way for the realization of high-performance optical nonreciprocal devices and provides opportunities for applications in integrated optics and quantum networks.

Received 30 April 2020
Revised 28 July 2020
Accepted 17 August 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.123901

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Photonics

Atomic, Molecular & Optical

Authors & Affiliations

Chao Liang¹, Bei Liu¹, An-Ning Xu¹, Xin Wen¹, Cuicui Lu ^2,3, Keyu Xia ⁴, Meng Khoon Tey^1,5, Yong-Chun Liu ^1,5,*, and Li You^1,5

¹State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
²Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements of Ministry of Education, Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Physics, Beijing Institute of Technology, Beijing 100081, China
³Collaborative Innovation Center of Light Manipulations and Applications, Shandong Normal University, Jinan 250358, China
⁴College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China
⁵Frontier Science Center for Quantum Information, Beijing 100084, China

^*Corresponding author. ycliu@tsinghua.edu.cn

Article Text

Click to Expand

Supplemental Material

Click to Expand

References

Click to Expand

Issue

Vol. 125, Iss. 12 — 18 September 2020

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Schematic diagram of the experiments [(a) and (c)] and the corresponding atoms’ energy level diagrams [(b) and (d)]. In (a) and (c), the cube represents the atomic vapor cell, and the rubidium (buffer gas) atoms are illustrated by yellow (green) dots in random motion along the direction of attached arrows. The switching laser (blue) and coupling laser (green) propagate in the same direction, while the probe laser (red) can be either copropagating (a) or counterpropagating (c). In the experiments, the three laser beams are spatially overlapped in the cell.
Reuse & Permissions
Figure 2
(a) Experimental results for the probe laser transmission spectra in counterpropagating cases ( $T_{cou}$ , red dots), copropagating ( $T_{co}$ , blue dots) cases, and without the switching and coupling lasers ( $T_{0}$ , gray dots). (b) Theoretical results corresponding to (a). (c) Isolation ratio (green dots, left vertical axis) and transmission contrast ratio (pink dots, right vertical axis) versus detuning of the probe field. (d) The bandwidth for isolation ratios greater than 20 dB [denoted by shaded regions in (a) and (c)] versus the probe laser power $P_{p}$ . In (a)–(c), the switching laser power is $P_{s} = 2.2 mW$ , the coupling laser power is $P_{c} = 1.5 mW$ , and the detunings are 0. In (d), the switching and coupling laser powers are optimized according to different probe laser powers.
Reuse & Permissions
Figure 3
(a),(b) Transmission spectra of the probe laser for different coupling laser power $P_{c}$ from 0 to 3 mW in the copropagating (a) and counterpropagating (b) cases. The switching laser power is fixed at $P_{s} = 2.2 mW$ . (c),(d) Transmission spectra of the probe laser for different switching laser power $P_{s}$ from 0 to 1.5 mW in the copropagating (c) and counterpropagating (d) cases. The coupling laser power is fixed at $P_{c} = 2.4 mW$ . (e),(f) Typical transmission of the probe laser versus the switching laser detuning $Δ_{s}$ (e) and the control laser detuning $Δ_{c}$ (f) in the copropagating (blue dots) and counterpropagating (red dots) cases.
Reuse & Permissions
Figure 4
(a) Transmission spectra of probe laser for the copropagating (blue dotes) and counterpropagating (red dots) cases with the probe laser detuning sweeping from $- 5$ to 10 GHz. (b) The corresponding isolation ratio of (a). The shaded regions denote the two nonreciprocal windows with isolation ratios greater than 20 dB. The switching laser power is $P_{s} = 2.2 mW$ , the coupling laser power is $P_{c} = 2 mW$ , and the detunings are 0. (c),(d) Energy level diagrams for the first (c) and second (d) nonreciprocal windows.
Reuse & Permissions

Physical Review Letters